Ad vectors have the ability to deliver transgenes to a variety of cell types, in vitro and in vivo, and unlike retrovirus based vectors, Ad vectors can also efficiently transduce mitotically quiescent cells. Therefore, the potential treatment of many different diseases, both genetic and non-genetic can be envisioned with the use of Ad vectors. For example, Ad vectors have been demonstrated to be capable of delivering genes to 1) liver cells for the potential treatment of many metabolic disorders, 2) muscle cells (skeletal and cardiac) for the potential treatment of myopathies and storage disorders, 3) brain and nervous system tissues for the potential treatment of neurologic diseases like Parkinson disease, and 4) respiratory epithelium for the treatment of pulmonary disorders like cystic fibrosis. In addition, many other common diseases like AIDS and various forms of cancer have all been demonstrated to be potentially treated by Ad mediated gene transfer strategies. While there is an enormous potential for the treatment of many human diseases, there are several problems with current Ad vectors that must be addressed before Ad mediated gene therapy becomes a clinical reality. The most serious problem with current Ad vectors is the transient duration of transgene expression after successful gene delivery into the tissues of immunocompetent animals. Other problems include the generation of replication competent Ad (RCA), and the inability of Ad vectors to carry larger genes or tissue-specific promoter/enhancer elements. This grant proposal outlines a series of experiments that will address each of the limitations of current Ad vectors. In so doing, we will isolate modified Ad vectors that are predicted to allow for longer durations of transgene expression in vivo, decrease the incidence of RCA generation, and significantly increase Ad vector carrying capacity. Initially, the modified Ad vectors will be analyzed in mouse models of liver and muscle cell gene therapy. The result will be the isolation of new Ad vectors capable of efficacious use in animal models of human disease, as well as for eventual use in the therapy of a great number of human conditions.